1. Field of the Invention
The present invention relates to an input device used in a variety of electronic apparatuses including a portable telephone and a portable information device such as a note type personal computer or a personal digital assistant and also relates to a method for detecting a position of contact between a resistor and a conductor of the input device.
2. Background Art
Recently, various electronic apparatuses including a portable telephone and a portable information device have become more functional. These electronic apparatuses use an input device having a planar pad or a trackball that is operated to move a cursor or a pointer on a display screen for input or selection of various pieces of information. Such an input device requires highly precise detection of an operated position or a press angle.
Referring to FIGS. 10 through 12B, a description will be provided hereinafter of such a conventional input device. FIG. 10 is a conceptual illustration of the conventional input device. Substantially ring-shaped resistor 6 includes, at its outer periphery, a pair of electrodes 7A, 7C projecting in a Y direction and a pair of electrodes 7B, 7D projecting in an X direction orthogonal to the Y direction. Substantially ring-shaped conductor 2 faces resistor 6 across a given clearance and includes, at its outer periphery, electrode 3 projecting in a specified direction. These electrodes 7A to 7D and 3 are connected to controller 10 such as a microcomputer. In this way, the input device is constructed.
A description will now be provided of a method for detecting the press angle when a specified part of the input device having the above structure is pressed.
As shown in a conceptual illustration of FIG. 11A, when the pressed position is, for example, point A, controller 10 applies a voltage with electrodes 7C, 7A rendered negative and positive, respectively, and detects, from electrode 3, a voltage corresponding to fixed resistance Rx between point A and electrode 7C. In this way, controller 10 detects point A, which is located fixed resistance Rx away in a clockwise direction from the negative electrode along the Y direction, or point B, which is located fixed resistance Rx away in a counterclockwise direction from the negative electrode along the Y direction, as the pressed position.
Next, as shown in FIG. 11B, controller 10 applies a voltage with electrodes 7D, 7B rendered negative and positive, respectively. Controller 10 then detects, from electrode 3, a voltage corresponding to fixed resistance Ry between point A and electrode 7D. In this way, controller 10 detects point C, which is located fixed resistance Ry away in the clockwise direction from the negative electrode along the X direction, or point A, which is located fixed resistance Ry away in the counterclockwise direction from the negative electrode along the X direction, as the pressed position. Based on these detections, controller 10 judges that point A, which is common to the detections in X and Y directions, is pressed and determines a press angle which point A makes. Based on the press angle, the cursor or pointer is moved on the display screen for input or selection of the various pieces of information.
However, there normally is contact resistance Rs where resistor 6 and conductor 2 contact each other, in addition to the above-described fixed resistances Rx, Ry of resistor 6. Using conceptual illustrations of FIGS. 12A and 12B, a description will be provided next of this case.
First, controller 10 applies a voltage with electrodes 7C, 7A rendered negative and positive, respectively. At that time, controller 10 detects, as the pressed position, point A1 located contact resistance Rs away from point A, namely located contact resistance Rx+Rs away in the clockwise direction from the negative electrode along the Y direction. Next, controller 10 applies a voltage with electrodes 7D, 7B rendered negative and positive, respectively, and detects, as the pressed position, point A2 located contact resistance Rs away from point A, namely located contact resistance Ry+Rs away in the counterclockwise direction from the negative electrode along the X direction. Controller 10 then judges that one of detected pressed positions A1, A2 is the pressed position. Such an input device is disclosed, for example, in Japanese Patent Unexamined Publication No. 2002-117750.
In the conventional input device described above, due to contact resistance Rs caused between resistor 6 and conductor 2, point A1 or A2 is detected as the actual pressed position, namely point A. This means that the detection of the press angle tends to involve an error.